Single crystal silicon essential to production of semiconductor devices and the like is obtained by being caused to grow into a crystal by a CZ method or an FZ method. As a raw material therefor, a polycrystalline silicon rod or a polycrystalline silicon block is used. Such a polycrystalline silicon material is often produced by a Siemens method (see Patent Literature 1 and the like). The Siemens method is a method of bringing silane raw material gas such as trichlorosilane or a monosilane into contact with a heated silicon core wire, and thereby, performing gas-phase growth (deposition) of polycrystalline silicon on the surface of the silicon core wire by a CVD (Chemical Vapor Deposition) method.
For example, when obtaining single crystal silicon through crystal growth by the CZ method, a polycrystalline silicon block is charged into a quartz crucible, a seed crystal is immersed in silicon melt obtained by heating and melting this to make the dislocation line to disappear (make this dislocation free), and after that, the diameter is gradually enlarged to become a predetermined diameter to pull the crystal. In this stage, if unmolten polycrystalline silicon remains in the silicon melt, this causes these unmolten polycrystalline chips to drift close to the solid-liquid interface due to convection, and induces dislocation occurrence, which causes the crystal line to disappear.
Moreover, Patent Literature 2 points out a problem that needle crystals are sometimes deposited in a polycrystalline silicon rod in a step of producing the rod by a Siemens method, when causing single crystal silicon to grow using such a polycrystalline silicon rod by the FZ method, individual crystallites do not uniformly melt in accordance with their sizes due to the aforementioned uneven fine structure, unmolten crystallites pass through the melting zone as solid particles to reach the single crystal rod, and the unmolten crystallites are incorporated into the solidification surface of the single crystal as unmolten particles, which causes defects to be formed.
Furthermore, Patent Literature 3 discloses a technique for selecting a polycrystalline silicon suitable for a single crystal silicon production raw material with high quantitativity and high reproducibility based on the knowledge that crystal grains in a polycrystalline silicon rod are not necessarily in random orientation, the degree of crystal orientation (property of random orientation) depends on conditions in polycrystalline silicon deposition, when using a polycrystalline silicon rod or a polycrystalline silicon block with relatively high degree of crystal orientation (relatively low property of random orientation) as a production raw material for single crystal silicon, partial unmolten portions sometimes locally arise, and this induces occurrence of dislocation, which possibly causes the crystal line to disappear.
Patent Literature 3 specifically discloses a method of making polycrystalline silicon into a plate-shaped sample, disposing the plate-shaped sample at a position at which a Bragg reflection from an <hkl> Miller index plane is detected, performing in-plane rotation with a rotational angle ϕ with the center of the plate-shaped sample as the rotational center such that an X-ray irradiation region defined by a slit performs ϕ-scanning on the principal surface of the plate-shaped sample to obtain a chart indicating dependency of the Bragg reflection intensity from a <111> or <220> Miller index plane on the rotational angle (ϕ) of the plate-shaped sample, and evaluating the degree of crystal orientation of the polycrystalline silicon based on the number of peaks (with an S/N ratio of 3 or more) appearing in this chart.
Further, Patent Literature 3 reports an example that when the number of peaks appearing in the aforementioned ϕ-scanning chart for a polycrystalline silicon rod is 24 quantity/cm2 or less, which is obtained by conversion on a unit area basis of the plate-shaped sample, for any of the <111> and <220> Miller index planes, there is no case where disappearance of the crystal line caused by induction of dislocation occurrence arises in producing single crystal silicon with such a polycrystalline silicon rod as a raw material.
However, along with a larger-diameter single crystal silicon ingot in recent years, it is being requested that the diameter of a polycrystalline silicon rod which is its production raw material also be larger to have a diameter of approximately 130 mm or more.